Structural studies on aryl‐substituted enaminoketones and their thio analogues. Part I. Analysis of high‐resolution ¹H, ¹³C NMR and ¹³C CP MAS spectra combined with GIAO‐DFT calculations

Abstract

A series of aryl-substituted enaminoketones and their thio analogues in CDCl(3) solution and in the solid state were studied by the use of high-resolution (1)H and (13)C as well as (13)C cross polarization magic angle spinning (CP MAS) NMR spectra in combination with gauge including atomic orbitals-density functional theory (GIAO-DFT) calculations performed at the B3PW91/6-311 + + G(d,p) level of theory using the B3PW91/6-311 + + G(d,p)-optimized geometries. The analysis of the (13)C NMR spectra in solution was done by using the Incredible Natural Abundance DoublE QUAntum Transfer Experiment (INADEQUATE) technique, whereas trends observed in the (13)C shielding constants, calculated for the compounds studied, were a great help in assigning most of the signals in the (13)C CP MAS NMR spectra. It was established on the basis of the experimental and theoretical NMR data that both groups of compounds exist in the form of Z-s-Z-s-E isomers in CDCl(3) solution as well as in the solid state, with the NH hydrogen atom involved in intramolecular hydrogen bonding. This conclusion is in agreement with the fact that some of the compounds studied reveal liquid-crystalline properties. Three-bond H, H and C, H coupling constants measured in solution played a crucial role in the structure elucidation.

Computational Prediction of1H and13C Chemical Shifts: A Useful Tool for Natural Product, Mechanistic, and Synthetic Organic Chemistry

“…Here, computed chemical shifts were used to revise the assignment of peaks observed for methyl bacteriopheophorbide a and methyl bacteriochlorophyll a ; the data for the former is shown in Figure . Many other examples of using chemical shift calculations to assign or reassign experimental spectra have been reported as well. ,− …”

The role of NMR in the study of partially ordered materials: Perspectives and challenges

“…6), showing that this procedure can be used where the chemical shift of a carbon has a different temperature dependence than the other molecular carbons. This example shows the high sensitivity of NMR to probe local molecular properties, which can then be interpreted with the help of molecular models or computational methods, as demonstrated by other recent research [66,215,[228][229][230].…”

Electron Ionization and Electrospray Mass Spectra of Diaryl-Substituted Enaminoketones and Their Thio Analogs

“…All studied compounds were synthesized according to the procedures described in the literature. 22 Results and discussion the structures of the aryl-substituted enaminoketones and their thio analogs which were subjected to mass spectrometry studies are presented in table 1. the results of the EI and ESI(+) measurements, limited to the molecular ion region, are presented in table 2. As it could be expected they depend on both the structures of the studied compounds and ionization methods used.…”

“…2,5,6 the enaminone system is often a crucial fragment of many complex, biologically-active compounds, such as purine bases, many agrochemicals and pharmaceuticals. [7][8][9][10][11][12] Numerous studies performed by the use of infrared (Ir), 13,14 ultra-violet (uV) 15,16 and nuclear magnetic resonance (NMr) [17][18][19][20][21][22] spectroscopies have shown that the enaminones undergo configurational and conformational changes and can exist in the form of various isomers depending on the solvents, temperature and concentration. Much less is known about mass spectrometry of these compounds.…”